decimal-scaled 0.4.1

//! Coverage for `macros/rescale.rs` — `rescale_with(mode)` on every
//! decimal width × every rounding mode, plus the scale-up overflow panic
//! path on D9 (the easiest tier to overflow at scale-up).

use decimal_scaled::{D9, D18, D38, RoundingMode};

const ALL_MODES: [RoundingMode; 6] = [
    RoundingMode::HalfToEven,
    RoundingMode::HalfAwayFromZero,
    RoundingMode::HalfTowardZero,
    RoundingMode::Trunc,
    RoundingMode::Floor,
    RoundingMode::Ceiling,
];

// ─── D9: scale-down with each mode, positive and negative ──────────────

#[test]
fn d9_rescale_with_all_modes_positive() {
    type D9_4 = D9<4>;
    type D9_2 = D9<2>;
    // 1.5050 → rescale to S=2 with each mode.
    let v = D9_4::from_bits(15050);
    for m in ALL_MODES {
        let r: D9_2 = v.rescale_with::<2>(m);
        // Result is around 150 ± 1 LSB depending on mode.
        let b = r.to_bits();
        assert!(b == 150 || b == 151, "mode {m:?} gave bits {b}");
    }
}

#[test]
fn d9_rescale_with_all_modes_negative() {
    type D9_4 = D9<4>;
    type D9_2 = D9<2>;
    let v = D9_4::from_bits(-15050);
    for m in ALL_MODES {
        let r: D9_2 = v.rescale_with::<2>(m);
        let b = r.to_bits();
        assert!(b == -150 || b == -151, "mode {m:?} gave bits {b}");
    }
}

#[test]
fn d9_rescale_with_exact_remainder() {
    // 1.5000 → S=2 = 150 (exact)
    type D9_4 = D9<4>;
    type D9_2 = D9<2>;
    let v = D9_4::from_bits(15000);
    for m in ALL_MODES {
        let r: D9_2 = v.rescale_with::<2>(m);
        assert_eq!(r.to_bits(), 150);
    }
}

#[test]
fn d9_rescale_with_identity_scale() {
    type D9_4 = D9<4>;
    let v = D9_4::from_bits(15050);
    let r: D9_4 = v.rescale_with::<4>(RoundingMode::HalfToEven);
    assert_eq!(r.to_bits(), 15050);
}

#[test]
fn d9_with_scale_delegates() {
    type D9_4 = D9<4>;
    type D9_2 = D9<2>;
    let v = D9_4::from_bits(15050);
    let r1: D9_2 = v.with_scale::<2>();
    let r2: D9_2 = v.rescale::<2>();
    assert_eq!(r1, r2);
}

#[test]
#[should_panic(expected = "rescale: scale-up overflow")]
fn d9_rescale_up_overflow_panics() {
    type D9_0 = D9<0>;
    let v = D9_0::MAX; // ~2.14e9
    // Scale up to S=8 (new MAX_SCALE) → multiply by 10^8; overflows i32.
    let _: D9<8> = v.rescale::<8>();
}

// ─── D18 / D38: every mode on a half-LSB input ─────────────────────────

#[test]
fn d18_rescale_with_all_modes() {
    type D18_4 = D18<4>;
    type D18_2 = D18<2>;
    let v = D18_4::from_bits(15050);
    let neg = D18_4::from_bits(-15050);
    for m in ALL_MODES {
        let r: D18_2 = v.rescale_with::<2>(m);
        let _ = r;
        let r: D18_2 = neg.rescale_with::<2>(m);
        let _ = r;
    }
    // Identity scale
    let r: D18_4 = v.rescale_with::<4>(RoundingMode::HalfToEven);
    assert_eq!(r.to_bits(), 15050);
}

#[test]
fn d38_rescale_with_all_modes() {
    type D38_4 = D38<4>;
    type D38_2 = D38<2>;
    let v = D38_4::from_bits(15050);
    let neg = D38_4::from_bits(-15050);
    for m in ALL_MODES {
        let r: D38_2 = v.rescale_with::<2>(m);
        let _ = r;
        let r: D38_2 = neg.rescale_with::<2>(m);
        let _ = r;
    }
    // Identity scale
    let r: D38_4 = v.rescale_with::<4>(RoundingMode::HalfToEven);
    assert_eq!(r.to_bits(), 15050);
}

// ─── Wide-tier rescale ─────────────────────────────────────────────────

#[cfg(feature = "wide")]
#[test]
fn d76_rescale_with_all_modes() {
    use decimal_scaled::D76;
    type D76_4 = D76<4>;
    type D76_2 = D76<2>;
    let v: D76_4 = D38::<4>::from_bits(15050).into();
    let neg: D76_4 = D38::<4>::from_bits(-15050).into();
    for m in ALL_MODES {
        let r: D76_2 = v.rescale_with::<2>(m);
        let _ = r;
        let r: D76_2 = neg.rescale_with::<2>(m);
        let _ = r;
    }
    // Identity scale
    let r: D76_4 = v.rescale_with::<4>(RoundingMode::HalfToEven);
    assert_eq!(r, v);
    // with_scale path
    let _: D76_2 = v.with_scale::<2>();
}

#[cfg(feature = "wide")]
#[test]
#[should_panic(expected = "rescale: scale-up overflow")]
fn d76_rescale_up_overflow_panics() {
    use decimal_scaled::D76;
    let v = D76::<0>::MAX;
    let _: D76<75> = v.rescale::<75>();
}